The present invention relates to a process for separating mixtures of olefins and normal paraffins. In particular, the process of this invention employs phenoxide catalyzed olefin alkylation of phenols as a means of harboring olefins during paraffin separation, and catalytic cracking as a means of regenerating the olefins after separation.
A valuable application of the separation process of this invention lies in the area of biodegradable detergents.
High-boiling linear olefins containing at least about 8 carbon atoms are useful in the synthesis of biodegradable surfactants. While several processes are available for dehydrogenating normal paraffins to prepare linear olefins, these processes actually result in the formation of a mixture of paraffins and olefins. For example, U.S. Pat. No. 3,248,451, granted Apr. 26, 1966, describes the use of a cobalt molybdate compound supported on alumina to catalyze the vapor phase dehydrogenation of long-chain normal paraffins. Despite the improved yields reported, the product of the cobalt molybdate process contained significant amounts of paraffin.
While, in some cases, the paraffin-diluted olefins produced by dehydrogenation can be used as such; in many cases pure olefins are required. For instance, olefin sulfonation to prepare detergent compounds having particularly desirable biodegradability and efficacy employs pure olefins. As a consequence of the need for pure olefin feedstocks several processes have been suggested for separating mixtures of olefins and normal paraffins. The most notable of these separations employ molecular sieves or selective extraction. For instance, U.S. Pat. No. 3,767,724 granted Oct. 23, 1973, describes the use of extractive crystallization to separate acyclic hydrocarbon mixtures of alkenes and alkanes; U.S. Pat. No. 3,355,509 granted Nov. 28, 1967, and British Pat. No. 1,107,307 describe the separation of acyclic hydrocarbon mixtures by molecular sieves; and Petroleum Processing, August 1949, describes the use of cyclic adsorption to separate hydrocarbon mixtures. In many instances even these procedures do not successfully separate a 100% pure olefin fraction.
Accordingly, there is a continuing need for a process for separating mixtures of olefins and normal paraffins.